1. Field
The present invention relates to methods of forming metal complex compounds, and to organic electroluminescence devices. More specifically, the invention relates to methods of forming fluorescent organic metal complexes, especially methods of forming fluorescent organic metal complexes for use in organic electroluminescence devices (light emitting devices, or EL devices), and with organic electroluminescence devices made by using such the organic metal complexes.
2. Description of the Related Art
In recent years, organic metal complexes have received attention as functional materials such as new display materials, memory materials, photosensitizing dyes and chemical sensor dyes. By using fluorescent organic metal complexes in particular in organic electroluminescence devices, the device efficiency has improved and performance enhancement has been achieved.
Organic electroluminescence (EL) devices can produce light emission of high intensity through the application of low voltage, and therefore attention has been given to them as promising display devices. One of important characteristic values of such an organic electroluminescence device is power consumption. The power consumption is expressed as the product of voltage and electric current, and the lower the voltage required for the device to attain a desired brightness and the smaller value the electric current is reduced to, the lower the power consumption of the device can be made.
Fluorescent materials have been used for the purpose of reducing the power consumption of such devices, and thereby improvements in device efficiency have been underway. As the fluorescent materials, iridium complexes and platinum complexes have been known (see e.g. JP-A-2001-247859 and JP-A-2007-19462), but they haven't allowed development of devices having compatibility between high efficiency and high durability yet.
In order to incorporate fluorescent materials into organic electroluminescence devices, there is a necessity to establish methods of chemically preparing metal complexes, notably fluorescent iridium complexes and platinum complexes, with high yield and high purity.
As methods for synthesizing iridium complexes and platinum complexes, there are the method of synthesizing them by allowing chlorine-bridged metal dimers and ligands to react with each other in the presence of a silver salt (Inorg. Chem., 1994, 33, 545-550 and J. Mater. Chem., 2003, 13, 80-83), the method of synthesizing them from chlorine-bridged metal dimers by way of β-diketoner containing complexes (Inorg. Chem., 2001, 40, 1704-1711), the method of synthesizing them by allowing tris(β-diketonato) complexes and ligands to react with each other (Inorg. Chem., 1991, 30, 1685-1687), and so on. However, decomposition products resulting from high-temperature reaction and impurities of starting material origin were included in the products obtained by using those synthesis methods, and they constituted a factor causing deterioration in durability of devices.
Complexes having 5-membered nitrogen-containing heterocyclic rings as partial structures of ligands, notably blue-fluorescent material-oriented complexes, tend to cause decomposition reaction at high temperatures, and a minute quantity of decomposed matter resulting from the reaction is apt to get mixed in devices. In addition, by-products tend to be formed (tend to take coordination forms other than intended ones). Therefore their yields are low, and besides, there were cases in which products themselves were not obtained.
Alternatively, methods of forming complexes by metal-metal exchange reaction have been also proposed. As to complexes having 5-membered nitrogen-containing heterocyclic rings as partial structures of ligands, however, high-acidity hydrogen atoms of the 5-membered nitrogen-containing heterocyclic rings cause exchange reaction with metals (Tetrahedron Letters, 1996, 27, 4095-4098), and therefore it has been difficult to synthesize complexes having intended coordination forms.